Conventional DC/DC regulators employ a bootstrap capacitor to supply power to a driver circuit of the regulator. The charge in the bootstrap capacitor provides a sufficient voltage across the capacitor to supply the driver circuit. However, if the voltage across the capacitor grows too large, this can result in improper or inefficient operation of the driver circuit. For example, if the voltage across the bootstrap capacitor exceeds the maximum gate-source voltage for the transistors of the driver circuit, poor operation of the driver circuit can result. Accordingly, a clamping circuit is employed to regulate the voltage across the bootstrap capacitor.
Some clamping circuits use a voltage comparator to sense the voltage across the bootstrap capacitor, and regulate the voltage based on the sensed voltage. However, the voltage on one of the electrodes of the bootstrap capacitor is typically high (e.g. up to 24 volts). Typical voltage comparators are unable to withstand such high input voltages. While a voltage comparator can be specially designed to accommodate the high input voltages, this can undesirably increase the complexity and cost of the circuit design. Accordingly, there is a need for an improved clamping circuit for DC/DC regulators.